<html>
<head>
    <meta>
</head>
<body>
<script>

    /**
     * Check if a string starts with $ or _
     * 检查一个字符串是否以$或者_开头
     */
    function isReserved(str) {
        var c = (str + '').charCodeAt(0);
        return c === 0x24 || c === 0x5F
    }
    console.log(isReserved('_aaa'))
</script>
</body>
</html>